I haven't used their EP ammo, but I've tried just about everything else in .380 while trying to solve the functioning problem with my uber-expensive Kahr P380!
The Kahr wouldn't chamber anything reliably - including ball, until I finally grew tired of waiting for it to "break in" and fixed the problem myself. The problem was the extractor was so stiff it sapped all the energy from the system and wouldn't allow the rim to slide up into place during chambering. I discovered the problem was the extractor spring was so long that when fully compressed into it's tunnel, it almost formed a solid column. After snipping a few coils the feed problem disappeared and the MAGAZINE dropping out problem suddenly appeared! While shooting Underwood +P ammo the magazine would pop loose causing a miss feed with each shot! At first I thought it was the +P ammo from Underwood, so I tried their standard pressure loads only to find the problem continued.
Granted shooting even standard pressure loads from a 10 ounce pistol is stressful to the gun.
So, again I finally got tired of the gun sitting on a shelf and decided to solve the magazine problem by replacing the factory wire spring with one from my own supply of a slightly thicker diameter. This solve the magazine popping problem!
Now, finally, after about 8 years of watching my expensive P-380 sit on the shelf I have it fully functioning to the level I'd trust my life.
In the process I tried Underwood's 90 gr. XTP in both standard and +P, and their 100 grain HC lead in both +P and standard, plus Ruger ARX 56 grain, and S&B.
NOW the gun feeds everything just fine....so there's that.
I know the "gel tests" indicate the .380 SD loads are on par with short-barrel .38 Spl loads, but this should only serve to make you choose a solid bullet that you have confidence will go deep.
I have little doubt the Underwood 65 gr. +P EP would do a decent job. My current "carry" load is the Ruger ARX which is very similar but has a round nose profile with deep-cut flutes in the nose.