Light wind sailing is THE most difficult to do 'right'.
The larger (cord length of) the sail the greater chance of a 'separation stall' ... an invisible stall because simply because the energy in the wind isnt sufficient to stay 'attached' and the 'flow' becomes 'detached' so that FRICTION cant transmit the energy of the wind into the sail.
The general answer is yes, the smaller the sail the less chance of 'separation'; BUT so too, will provide less surface area when the flow IS attached - a conundrum.
Mother nature, has already figured this out - long thin high aspect wings for soaring, short low aspect wings for high speed/maneuverability (eg. F-104 and goshawks). If one considers the top class high end mega-race boats ... jib will be somewhere near 120%LP 'max'.
More importantly, the shape of sail becomes vitally important, especially the amount of draft, ... even on a 2 dimensional shape such as sail that has essentially NO 'thickness'.
Air flow stays 'attached' when there is sufficient energy in the air flow; however, when the air flow has to change direction, to stay attached it must have sufficient energy to do so; a flatter sail (with less change of direction) requires less energy for the air flow streams to stay attached.
In light winds across a 'rounded luff shape' and at the point of maximum draft when the draft is 'full' will have the most difficulty in staying attached. .... so its more important to have the right 'shape' in light winds for considerations of 'separation' than (still important) the 'length' that airflow has to travel.
Also too, the distance that the so-called slot is operating 'should' be optimized so that the combined flows of jib and main are optimized .... the lower the wind speed, the closer the jibs leech should be to the point of maximum draft of the mainsail (and vice versa) ... such optimum distance of the 'slot' will provide 'faster' apparent wind to both sails.
Rx: for 'light winds':
• less rounded luff shape (less halyard tension),
• FLATTER shape/less draft, on most boats probably a 120-130%LP jib,
• the TOP mainsail batten aft end approx. parallel to the boats centerline,
• the traveller at the CL .... or higher IF the wind has a lot of 'twist' (but the aft end of the boom NEVER above the boat's centerline)
•..... and ALL tell tales flying perfectly (especially monitoring for separation stalls on the leeside/leeches).
••• Lastly, pull in the jib's barberhauler (to set the 'slot distance') while watching the speedo ... the correct slot distance will be found AT the max. speed (expect a slight 'backwind' to show on the main).
• Recheck to make sure ALL tell tales are 'perfect' when at 'max' speed, readjust SHAPE if necessary.
Rx2: KEEP THE SPEED UP
• ... so that apparent wind is the highest (more energy);
• dont 'drag the rudder' ... may have to rake the mast more forward to get to an 'almost' neutral rudder pressure;
• use only finger tips on the tiller/wheel and use a bit of increased mainsheet tension (slight hook to weather on mainsail leech) to help 'steer' the boat through a tack - dont 'jam' the rudder over when tacking --- light 'pressure' on the helm to turn the boat;
• open the traveller a wee bit after passing the 'eye of the wind' during a tack to better accelerate back to optimum speed on the second half of the tack;
• once back up to speed then 'turbo sail' (do search in the sail trim forum for same)
Rx3 (not to be used when racing, or instant DSQ!!!):
To enhance acceleration after tacking, heel the boat to leeward, FAN the mainsail by 'pumping' IN/OUT on the mainsheet (traveller on CL) while watching the speed for max. attained, then bear off slightly, and then 'turbo sail' ... very illegal when racing, very effective on a light weight and broad beamed boat. When combined with a slow 'roll tack' and 2 'pumps' on the mainsheet ... usually can gain 1 boat length.
Rx4:
when completing a windward 'leg', POWER PINCH to the layline by pulling in on the mainsheet 'hard' to 'cup the leech of the main to windward' (set the 'flaps' down for high lift low speed sailing) ... start POWER PINCHING 'several boat lengths' from the layline.
The 'lift' will save several boat lengths on the 'next' leg. Dont stall the boat speed when doing so. POWER PINCHING to the lay-line will cause tremendous 'lift' to weather using the boats previous momentum and the exaggerated DRAFT induced in the sail by 'leech hooking' ... save enough 'momentum' to make the turn/tack, dont 'jam' the tack with aggressive rudder movement which only 'slows' the boat, and then power-accelerate out of the tack to quickly regain the highest apparent wind.
Success in light wind sailing/racing .... KEEP YOUR BOAT SPEED AS HIGH AS POSSIBLE .... and enjoy the increased apparent wind - as youre now 'making your own apparent wind' with the boat speed. If you keep your boat speed 'up', you 'can' use a larger cord length sail and it wont 'separate stall' as easily because of the enhanced wind energy because the boat itself is moving 'faster' and is helping to generate its own 'apparent wind'!
hope this helps.