If you feel that the input level on the Analog Heat MKI/MKII is lower than expected, there is a technical reason for why it is like this. Then input level on the Analog Heat is set like it is by design.
The Analog Heat attenuates (lowers) the incoming signal to create headroom for the distortion circuits and the filter. If it didn't do that, the levels would be too high and cause internal clipping if you use heavy distortion and turn up the resonance on the filter.
You can always use the LEVEL parameter to gain the level back up if you feel that the volume is to low after passing through the distortion, filter, and EQ.