the close variant problem is real and getting worse, but one thing nobody mentioned is the device bid splits. desktop and mobile convert totally different on bing imo, especially older crowd... i usually start mobile at like -20% and adjust from there once i got data. saved me a decent chunk.
also dont sleep on dayparting. bing traffic on weekends is weird, lot of bored browsing not buying. i pull back spend sat/sun on most lead gen accounts and roi jumps.
what worked for you might depend on vertical tho. b2b the linkedin layering people keep bringing up is solid but for ecom its kinda useless, just adds noise.