Here's a chart that shows the appropriate values of R1, R2 and C1 compensation components for the Pi crossover. The way it works is the level of attenuation shown in the "dB" column is what the circuit presents to the tweeter below mass rolloff. Above that, attenuation is removed at 6dB/octave. So if you use R1/R2/C1 values that give 10dB attenuation, the tweeter will be -10dB from crossover up to 6kHz, at 12kHz it will be -4dB and by 20kHz there is no attenuation at all.
dB R1 R2 C1
====================================
6dB 12 ohm 30 ohm 0.47uF
8dB 12 ohm 20 ohm 0.47uF
10dB 16 ohm 16 ohm 0.47uF
12dB 25 ohm 16 ohm 0.47uF
14dB 30 ohm 14 ohm 0.33uF
16dB 40 ohm 12 ohm 0.33uF
18dB 50 ohm 12 ohm 0.22uF
20dB 75 ohm 12 ohm 0.22uF
====================================
