Show photo.
Water flow from shower head is only good as it is. Any addition piping will hinder the flow without a pump.
Like what mini orchard has commented, showing us your installation picture will better help us understand what problems u are facing.
Regardless, just backtrack and investigate which component is slowing down your water flow, assuming your original water source has good water flow, as what u have mentioned.
1. Remove pipings from water source to water heater, double check if your original water source is still strong. If yes,
2. Connect water source to stop valve, remove stop valve from water heater's inlet, check if your original water source is still strong. If no, the stop valve is what slowing down the water flow. If yes,
3. Connect stop valve back to water heater's inlet, remove water heater's outlet hose, check if your original water source is still strong. If no, the water heater is what slowing down the water flow, maybe something stuck inside. Get Midea service team to check. If yes,
4. Connect water heater's outlet hose, remove shower handset. Check if your original water source is still strong. If no, the shower handset is what slowing down the water flow, maybe something stuck inside.
. It's been a long time since my last reply.
I manage to solve the problem. Caused by some hard mineral from the pipe stuck between the inlet hose and the water source. Maybe when the contractor remove the shower and turn it into inlet they didn't notice it. I remove the inlet hose from water source and notice it stuck on the filter. Cleaned that and my water pressure is back to normal.