The specs for MPE are here:

https://www.midi.org/specifications/midi1-specifications/mpe-midi-polyphonic-expression

Page 14 describes the pitch bend functionality. I get the general idea, but I'd have to see it in practice to fully understand 😉 I didn't know it was even a thing until I read your question.

When a receiver receives an MPE Configuration Message, it shall set the Manager Channel Pitch Bend Sensitivity
to 2 semitones, and the Pitch Bend Sensitivity of every Member Channel to 48 semitones. The values may
subsequently be changed at any time using Registered Parameter Number [RPN] 0, in accordance with the MIDI
1.0 Specification. Because the Zone Pitch Bend Sensitivity on the Manager Channel is controllable independently
from that of the Member Channels, setting them is accomplished as follows:
• Manager Channel Pitch Bend Sensitivity is set by sending RPN 0 to the Manager Channel.
• Pitch Bend Sensitivity on the Member Channels is set by sending RPN 0 to every Member Channel
individually.

The use of RPN 0 presents the option of supplying a less significant byte (LSB), for conveying the microtonal
fractions of Pitch Bend Sensitivity. It is recommended that MPE Devices use an integer number of semitones for
the range and either transmit the LSB as zero, or not transmit it at all so that the receiver infers zero. MPE Devices
may still choose to respond to 14-bit Pitch Bend Sensitivity messages for compatibility with other equipment.

To simplify interface design, MPE Devices may limit their communication to a whole number of semitones
between 0 and 96. (At 96 semitone resolution, the granularity of 14-bit Pitch Bend data is still smaller than 1.2
cents.)

An MPE Device may send Pitch Bend messages on both the Manager Channel and on Member Channels. On the
Manager Channel, Pitch Bend is typically performed through movement of a global control (for example, a pitch
wheel or a tremolo bar). On Member Channels, Pitch Bend is typically performed by the movement of a single
finger on the playing surface

This article has some good information that may help? The Purple Rain video is phenomenal. In my mind, that's always how I wanted my MIDI to be.

https://www.midi.org/midi-articles/midi-polyphonic-expression-mpe