He may need longer sleep during the day due to nights, he's getting 11+ at night but with the 2 feeds so not a full 11hrs IYSWIM? I think it probably depends what you want to do about the night feeds. I know they say that night sleep is more restorative than daytime but if you feel he needs to keep the night feeds at present due to milk intake etc.. then I would be tempted not to cap day sleep unless you are hitting problems by doing so (EW, nap/bedtime resistance etc..). You may find that once he drops/you wean NF then his nights shorten and you need to look at capping at that point to address it. The other thing to consider is how he is during the day? Is he quite a settled, happy little chap or does he get cranky, that would push me more towards working on dropping NF to improve night sleep which may involve capping one of the naps. But as I said in my oppinion if it isn't broke don't try and fix it. If he functions fine on his current night sleep and uncapped naps don't create problems I would roll with it, he may just be high sleep needs (lucky you!). I have a LSN 1 year old so am not speaking from experience just what I would do in your situation. Hope someone with BTDT experience can offer their pearls of wisdom!
Have you tried dropping the df at all or are you keeping it due to weight gain/reflux issues?