With a single driver you should pick a measurement distance close to your listening distance. Set your mic height at the center of the tweeter and center it between the ribbon and the woofer line. If the distance is to great to get good response curves then move in a little closer. Choose a topology that will allow you to vary the ribbon level without affecting the transfer function of the high pass section. It may be that the woofer line will be higher in level, if so, try to manipulate the DCR of the low pass inductors to lower the woofer level. Hope this helps.