Its hard to describe the after taste, Its not sweet, sour, or astringent. Its just a very dull bland aftertaste at the end and not very crisp. I really notice it with lighter brews but then i started to pick up on it with all my brews. Its a very 1 dimension taste and that's why i thought it'd be a mash PH issue. It still hasn't gone away since ive been using a ph meter to hone in my levels.
Re-reading through John Palmers chapter about water/mash ph level again i notice my sodium level is very low. He says around 50-70ppm will really make the flavors come out and pop. It sounds like you are getting a good grasp on Water Chemistry. I would suggest downloading Bru'n Water to dial in your process based off of your beer style and also reading additional information from the Water Knowledge section. Great tool and any questions about the sheet is usually answered very quickly in the Brew Science sub forum by Martin. So i recently brewed a pale ale and got my sodium around 50ppm, chloride 100ppm, sulfate 250ppm. This brew turned out perfect and that dull after taste is gone. So, this sounds like you've answered your own question. I typically adjust my Sulfate level to 200+ PPM and check that the Sulfate/Chloride ratio is greater than 2.0 for IPA's and Pale Ales.
I normally mash in a igloo cooler and batch sparge boiling on a bayou turkey fryer sp10. This last brew i did BIAB and wrapped in blankets then i brought it to a very low almost border line simmer boil being on my stove top. It sat in the primary for 18 days before i keg. I really think its the sodium level but till i do another batch i wont know for sure.
I use to fine my brews with gelatin but haven't recently because i thought it was stripping my brews of hoppy goodness. I do cold crash my beers down to around 35 for a week before i keg.
I've always kept my brew on primary 20-30 days before keg or bottling.
THIS is a solid practice for the exact reasons you mention below. I personally would not change this. No need for secondary.
Mainly from reading that at such a smaller volume you don't have to worry about yeast cells bursting within 3 months, Larger commercial ferm tanks being so large have a lot more weight being pushed down on the yeast cake. Also ive seen a side by side experiment one brew racked into secondary and the other staying on primary. The brew in the primary cleared up quickly and had a smoother profile. Unless your planning on conditioning for couple months i feel its a risk to contaminate your brew and your missing out on some scrubbing and cleaning the yeast can be doing.