In my opinion collection is not something that can be forced on a horse, especially by the use of side reins. I believe the use of restrictive equipment causes the horses natural movements to be..., well restricted.
Collection should be about self balance, self carriage, free movement, and not about setting a horses head in a fixed position.
The horse shows his most beautiful movements when moving at liberty, while he is having fun and playing. If you can have fun together with your horse, do things with him instead of to him, it's pretty amazing how easily they collect all by them selves. Besides; it's pretty fun and a great way to warm up for both the horse and the rider.