ok, i need to see your models. post the xlights_rgbeffects.xml and also tell me the model name.
for example suppose you have a model that has 300 channels and set the model to start at channel 1. it would fit within the 1200 channels you defined. But what happens , for the same model,. you say it starts at channel 1000. the model needs channels 1000-1299.. you would get a message saying it is expanding the defined channels to have enough channels to cover the models needs.