Scope is scope
Your scope, with chain & nylon rode, should be the same as their scope, even with all chain rode. Those with all-chain can try to "get by" with less scope than you, as long as the wind in your anchorage remains low all night long.What you suggest adding to your system, in an attempt to limit your swinging room is called a "kellet" or "sentinel". I have used such a system on my boat, ABI makes an attachment that will slide down your rode (for sale at Sailnet) to which you can attach a weight and a retrieval line. I used a 10 lb. mushroom anchor as the weight. The ABI attachment is smooth and will resist chafing your rode.The big problem that I encountered using a kellet was from other boats who entered an anchorage after I was anchored. The other boats attempt to estimate the position of your anchor based on the angle that your rode enters the water and the water depth. Using a kellet will mask that, as the weight sometimes causes your rode to even hang straight down into the water on windless days (the weight is suspended off of the bottom). Other boats would sometimes anchor much closer to my boat than they normally might have had I not used a kellet (much too close for my comfort). I'd even been accused of not knowing how to anchor or what scope was (by powerboaters naturally). No one knew the terminology, kellet, sentinel, how it all works.... But there was a definite relationship between having anchored neighbors too close, and using the kellet. When I didn't use that system, I didn't have the problem nearly as often.