radiant concrete qestion

I searched on here and other sites to no end. I will get some pictures up later if I can.
I have a mixing valve on the supply side and my question is will the boiler (Aquatherm wood eater) recover with the supply being mixed with the concrete return to 115 or if I turn it up to supply 130is so the return is running hotter not dumping all the cold into the return. If I do turn up the mixing valve hot water is bypassing the valve and heating up my return pipe to a point where I can not put my hand on it. So I am thinking that it is not mixing at all going into the floor. I know the floor is well insulated from the standpoint that I shut it off last night and in the morning I only lost about 5 degrees in the kennel, it's just that when it runs it takes a long time to get up to temp on the thermostat to shut it down. I have made progress with this as in years past I didn't even bother with the floor heat and just used a hanging heater. I will see if I can get a picture of what I am talking about. I should mention that when it is running and the slab is warm if my supply is 115 my return is around 100 and when I crank it up my supply is 140 and return around 120 before the mixing valve but much hotter going back to the system after the valve.

Thanks
Tom

ok I hope the pics turn out. I will try to explain them if they do.
This unit also feeds our house with a HX in the forced air furnace which works great by the way.

so the supply is going into the mix valve then to the pump for the in floor heat. The sideways picture is of the back of the aquatherm with the main pump for the house. I have the circuit for the hanging heater in the kennel shut off which you might be able to see in the pics.
Does this help at all.

Yes I think if the return temperature was higher then the boiler would work better. Now whatever the return temp is it is getting dumped right into the return.
Another question is: is it better to adjust the mixing valve for hotter water going in the slab but also bypassing the mix and increasing the return. I can do this if I turn it to #4 or #5 on the valve. The hot supply goes right through the valve and into the return.
This is for a kennel and the way the guy designed to floor heat (with cold spots for the dogs to sleep on) I think I don't have enough tubing in the floor. The guy that poured the concrete even questioned the amount of tubing. It sucks but the guy said it would work.