Small signal Forward converter
We can certainly compare the ac response of the forward converter modeled with the CM PWM switch model by running a SIMPLIS simulation. For that purpose, one of the 60+ free templates I posted can be a good candidate for this experiment:

In this example, you see that slope compensation is implemented in a different way than I used to do. With this approach, the added slope matches the theoretical numbers. I transform a 1-V sawtooth affected by a coefficient \$k_r\$ into a current that I inject into a 1-\$\Omega\$ resistance. This current is added with the inductor current scaled with the sense resistance value used as a coefficient. By adjusting \$k_r\$, I can tailor the exact amount of the injected slope. For instance, with a 10-µs period and the 1-V peak value, the artificial slope is 1/10µ = 100 kV/s. If I want a 16.8 kV/s slope, simple set \$k_r\$ to 168m and you are all set.
It is easier to do with the SPICE average model as there is a parameter than I can set to 16.8 kV directly. Please note - and this is important - the magnetizing current in a forward converter acts as a free compensation ramp. If you add a 16.8-kV/s slope, the total compensation is the sum of the magnetizing ramp and the external value. If SIMPLIS does it naturally because it is a cycle-by-cycle simulation with a transformer featuring a magnetizing inductance, you have to account for this contribution in the average model:

If you now run both simulation engines without an external compensation ramp (but the magnetizing ramp is always there), then you see the below plots with a good match between SPICE and SIMPLIS:

When I set the external ramp to 16.8 kV/s, as expected, the double poles are damped but matching is still very good:

In a practical realization, the recommended option based on the drive signal is a good and robust way to provide external ramp. However, depending on the loading of the ramp generator, you may end up with a slightly different compensation level which is not a big deal in reality: there is no need for an absolute ramp amplitude precision for a good compensation. Resorting to a more precise implementation with the current source is a possible option when one wants to compare responses between models.
By the way, you can see a magnitude and phase deviation between SIMPLIS and SPICE. This is due to the approximate modeling of the sampling effect in the inner current loop. You can have a look at a recent article I recently released on the subject which explains how this loop has been modeled by Ridley. If you adopt the real sampled equation, then SIMPLIS and SPICE perfectly agree well beyond \$\frac{F_{sw}}{2}\$. See here for more details on how to do it.