I was having the same problem - medium gel's being a tad too small & the large ones being a tad too big - so i started swapping tips/sleeves/foamies/flanges/etc from some of my other IEMs & found the following tips to fit perfect:
- Shure's SE- series sleeves (& most of their E's, i's & SCL's)
- Sleek's SA-6 flanges
- Futuresonic's Atrio M5/8 plugs
&
- Comply T-100's - P's also, but you'll need to force them just a little..
Personally I like the Shure EABKF1-10 (medium)'s best, they are practically the same size as the Comply t-100-/P mediums, but to me these feel just a bit more luxurious (they're more conical so they suit me better), & they're black..
I also find these foam type tips to reduce quite a bit of microphonics (or it's the thin-nes of the Klipsch gel that enhance microphonics?), plus they increase the the depth of the lows a little more to my liking.
The slightly thicker double/triple flanges I found to be nice fitting & sounding aswell but because
i'm not using X-10's but Custom-3's they are just too long (they make the Custom stick out too far), but my guess is that they will fit the Image's just fine. [size=xx-small]According to Klipsch' tech support the Image's & Custom's use identical gel's, so not to worry.[/size]