If one block have its exclusive carried textures, when block resolution is bigger than carried item in resource pack, the size in item frame will be smaller, when carried item resolution is bigger than block, the size in item frame will be bigger.

if an HD texture pack only includes the carried texture, when put the item into frame, the size will be super large. For example, the sceenshot below: the pack only includes HD candle items but candle blocks are missing.