Does the seat pan feel comfortable and fit your shape?
When you sit in the chair, the seat pan should be at least one inch wider than your hips and thighs on either side. The seat pan should not be too long for your legs otherwise, it will either catch you behind the knees or it will prevent you from leaning fully back against the lumbar support. Most ergonomic chairs have a seat pan with a waterfall front that prevents the seat from catching you behind the knees. The seat pan should also be contoured to allow even weight distribution and it should be comfortable to sit on.