Have never had any problems with chain slippage on either of my bikes and they’re both horizontal drop out. 1×1 is running a Surly Tugnut. Standard Cotic tensioner / gear hanger jobbie on the roadrat.
I’d say that if the chainline and tension is correct, and there’s plenty of wear in the chainring and cog then there is no way you should be dropping so much.
Is there a chance that chainline may be an issue if you’ve recently fitted a new chainring?
If tension is a problem, are you running standard QRs? If so, consider swapping to a nutted axle or ones with an allen key bolt.
Interesting to see recent comments on this and other threads about the SRAM PC-1 stretching – Has the design changed recently or something?
I’ve swore by them for years – the same one has been on my 1×1 for donkeys and been really punished but it’s been fine barring an initial few adjustments during the first “bedding in”.