The other consideration for the board width is the size of the birds. My LB's prefer to hope off, not use the ramp. They need some landing space. My board is also around 30" tall...good height for me.
My birds (ISAs, Maran mixes, Chanteclers) mostly do not use the ramp to dismount but they fly/glide rather than hop off. The glide path is 45 degrees so they need floor "length" that is at least the height of the DB; too little space equals crashes. Hard floor surfaces are BAD, hard on feet and legs; I use deep bedding (pine shavings plus straw) that is at least 8" deep, provides a perfect cushion in addition to low cleaning maintenance; my bedding is close to a year with no clean out, daytime droppings (very minimal) dry then disappear (chickens turn the bedding over several times a week), no smell and DRY.