I've had a 2.5-3" Bicolor Blenny for months in my 125gal, 6' DT and recently wanted to add a 2" (slightly smaller) Tailspot Blenny. I asked the LFS guy (who more often than not tells me not to buy something) if they would work together, and he said yes. Even though they have the same shape and "niche", I was hoping that the big difference in color and pattern would help.
Nope. Ever since my GSM clown died about a month ago, the Bicolor Blenny has ruled the 6' long DT with an iron fin. As soon as the Tailspot Blenny would come out to try and graze, the Bicolor Blenny would chase it back into its hole which made the Tailspot Blenny want to hide in a top, back corner (making me scared it was going to jump out). I had to use a piece of rigid air tube to "show the stick" to the Bicolor Blenny. I never actually touched it with the tube, but now all I do is point it at the tank and the Bicolor Blenny retreats.
Now several weeks later and the Tailspot Blenny is doing fine. It grazes and roams at will, and the Bicolor Blenny only harasses it sometimes when I feed (I guess it still gets jealous).
Anyway, that's my story. I hope it helps.