More powerful amp needs to be turned up higher than lower powered amp?

Nothing to worry about. I've experienced the same and the converse. Volume control designs are varied, scales vary (numeric or -dB) and sometimes are switchable too.

The hi end of rotel is michi and it's all great equipment and built well. I have the complete rotel 1590,1090, and thier cd players.they work fine and yes it's the design and gain and volumn design.in general the higher wattage amps will play on lower volumn and have more headroom or transients.that means there is alot of acceleration left prior to running out of steam or clipping ie distortion. Recently the government stepped in and made standards for measuring the standards of amplifiers  they have not done that for decades. Enjoy your new stuff it's a great product.

The volume control on an audio amplifier uses a logarithmic (audio) taper, so the knob position is not linearly related to signal level or power output. As a result, a 50% volume setting does not correspond to 50% of the amplifier’s power delivery. This could be indicative as to the discrepancy you see between the two amps.

Amplifier specifications usually list a category called ’Input Sensitivity’. It consists of a voltage level required to give the rated power output. The other input specification is the ’Input Impedance’ which is a different measurement of the input which works in conjunction with the sensitivity. Both should ideally be optimal for the partnering equipment.