I guess you mean 100mm deep and wall mountable? Otherwise would be ideally looking at the RXC to match. I would suggest the best match tonally would be the Apex A40, if you can't stretch to that the MA Radius R250 HD, but you would be best advised to stick with the RXC.
You may have a hard job finding one assuming you mean 4" high. How about a Monitor Audio Radius R225HD at around £250, (WxHxD) 125 x 610 x 106 ( 5" high if laid length ways, sorry yes a bit over size ), available in various colours including black.
As this is from the same company, it should be a better tonal match with your existing speakers, as opposed to mixing brands/makes. It is always preferable to have all the same if at all possible, to keep a well balanced soundstage.
thx for your reply's, and yes i do meen 100mm high, although this is not exact, got a new stand for components and tv, tv floats above top shelf (cantilever) but this did not arrive with the stand so i am only guessing at this point. Have been looking at the dynaudio xcite x22 which is at 5", this is over budget but the centre is one of the main speakers for H/C, not sure about the tonal matching though, anyone got one, that can comment?