Shorthanded WTSD% and Standard Deviation

[weevil]

What is the correlation between these two stats? I keep trying to bring my WTSD% below 40%, but I'm always at that range. As well, my standard deviation has always been a little over 20BB/100. Both of these stats seem to fall just outside the upper range of what is considered part of a winning style, yet I've managed to be a decent winner over a very large sample. Everything else seems normal statwise:

VPIP: 27%, PFR: 20%, AF: 2.75, W$SD: 47%, W$WSF: 46% - I'm averaging 1.8BB per hand on non-folded high card showdowns, and my river fold is at 38%.

So even though I'm going to showdown often, it's not with poor high card calldowns or a failure to fold clear losers. What gives? And why is my Std. Dev. so fing high? I've had a few 150BB swings, but mostly my earnings haven't seemed that streaky.