Several things could be working separately or together to give you (apparently) less contrast with the larger size paper.
First, if you're making an 8x10 print on the 8x10 paper and an 11x14 print of the same negative on the 11x14 paper, you are not making a real comparison. Larger prints almost always need a bit more contrast to look "right" than smaller ones. It's a characteristic of the way we see, not a difference in the paper. For a true comparison, you should make an 8x10 print on the 8x10 paper and then make that exact same-size print on a piece cut from the 11x14 paper.
Different paper batches differ slightly in characteristics, including contrast.
Paper loses contrast (and fogs) with age. You may simply have older, less-contrasty paper...
There may be more fog from scattered light/unsafe safelight, etc. at a greater degree of enlargement and the appropriately longer exposure time, which will affect contrast of the final print.
I assume you are using the same enlarging lens for each print, but if not, the choice of lens can definitely affect contrast of the print.
I have never tried to make a larger version of a smaller print by simply scaling up and using the same paper grade. I always start from scratch, albeit using the smaller version as a guide for manipulations, etc. and determine which grade I need as usual. Hoping for a match from different packs of paper is wishful thinking.
Best,
Doremus