Put that heat mat under your prop tray and dome and the temps inside the dome should be slightly higher than ambient.
Another way to cheat is to put your prop tray on a milk crate and put an incandescent light under the crate for bottom heat.
In questionable cloning conditions, fungus becomes a threat, and you should use a cloning solution that contains fungicide. Clonex and Olivia's do NOT. Dip-n-Grow and Rootone DO. Dipngro is better than rootone IMHO but as always, use proper cloning technique and keep your equipment and tray/dome combo CLEAN (Scrubbing Bubbles is a good cleaning agent because it foams and you can see if you missed a sopt).

Limited in height? Train your plants to spread out and lay flat. You can even toss a net over them and then let the buds grow up and through when they form.