That bilge reminds me of that of the Hunter 27, which is not very deep. It looks like it has about 1/2" of standing water where the float switch is unable to activate. Allow me to suggest an electronic pump. Rule has a 500 GPH model controlled by a computer chip. It turns itself On every two minutes for a few seconds and if the impeller encounters water resistance it will continue pumping until it gets the water out. If no resistance it will turn itself Off for another two minutes. The advantage is that it gets more water out, the level will go down until the pump just encounters light resistance. Another advantage will be that it does not depend on a float switch which chances of getting fouled are much larger. Since once it turns Off it will not come On for another two minutes any water flow back from the discharge line will not induce continuous cycling. Even though it may seem to run very frequently the power consumption is quite low as it draws very little current and it only runs for under 2 minutes every hour. The downside is cost, the last time I checked they were selling for around $50.