2-3 ft sounds good, and even at 3 ft you'll get some overlap of the stems once the clump gets mature & starts to spread.

Let your stems get to about 12-15" tall, then cut them back by half or more. I usually use a bypass pruner to snip just above the second or third healthy leaf (from the soil line). You can even pinch the new stems a second time later if you wish. Pinching increases the number of secondary stems (and tertiary stems if you pinch twice), as well as the number of blooms. It also increases the strength of the stems and makes them more resistant to the combination of wind/rain that tends to force unpinched plants to lay over.

Al

Thanks, Al. That really helped!