The lash does look a little tight. Can you put any fingers between the lash and his/her cheekbone? If you can, it will be fine. You could get a saddler to stretch the lash for you! My saddler says he can stretch a browband by an inch!! :D
Hi,
I hire out Micklem bridles and it does sound that you need the next size up which would be standard. The standard size is longer rather than wider. Hope this is helpful!