Could it also be the the effective radiated power of 129 is lower than 110 and 119.
I suppose that depends on where you live. Overall though, Ciel-2 is just as powerful as the rest. For example, on most TPs with my 1000.2, I get about 77-78 on 110. On 129 TP 21 I get 77-80. On 119 I get 82-86 on the strongest TP. The only reason 129 appears to be "weaker" on most transponders is due to 8PSK modulation vs QPSK modulation. TP 21 on 129 is still QPSK, thus it has similar readings to 110/119. TP 7 on 110 is 8PSK, and you will find that it has similar readings to most of 129's TPs. This doesn't mean that the signal is actually weaker, it's just that 8PSK uses different FEC algorithms.
The signal strength meter on the receivers would be more accurately described as a signal quality meter. I have found though that as the actual signal strength drops, the gap between 8PSK and QPSK readings gets narrower. QPSK is really only marginally more resistant to rain fade. So this brings us back to other factors, such as, the elevation of 129. The lower elevation means more atmosphere for the signal to travel through, and again, more chances for rain fade.
Sooner or later 110/119 will be switched to 8PSK, as soon as DISH gets rid of all QPSK (legacy) receivers out in the wild. When this happens, 110/119 will have comparable "signal strengths" according to the receivers' meters. The lower numbers don't necessarily actually mean that there is in fact a weaker signal.