Let's look at Telstra:Closing sp 18/2 (last day cum dividend)...

Let's look at Telstra:
Closing sp 18/2 (last day cum dividend) $2.96
Ex-dividend 21/2 $2.80
22/2 $2.80
23/2 $2.79
24/2 $2.77
25/2 $2.82
If we take the lowest sp of the week after ex
dividend, 24/2 ($2.77) from the last day cum
dividend ($2.96), the difference is $0.19, or
approx 6.5%.

Granting SIP goes up to 0.50 (conservatively), retrace
of 6.5% will mean 0.467cps, say .45cps.

Definitely NOT low 30s unless you want the price to go
down so you can buy some more...