Customise the image size used for Image Choices

custom_image_choices_size.php

<?php
add_filter( 'gform_pre_render', 'custom_image_choices_size' );
add_filter( 'gform_pre_validation', 'custom_image_choices_size' );
add_filter( 'gform_pre_submission_filter', 'custom_image_choices_size' );
add_filter( 'gform_admin_pre_render', 'custom_image_choices_size' );

function custom_image_choices_size( $form ) {

	foreach ( $form["fields"] as &$field ) {
		if ( property_exists($field, "imageChoices_enableImages") && !empty($field->imageChoices_enableImages) ) {
			foreach( $field["choices"] as $i => $choice ) {
				$id = $choice["imageChoices_imageID"];
				$field["choices"][$i]["imageChoices_image"] = wp_get_attachment_image_src($id, 'full');// replace "medium" with whichever size you need
			}
		}
	}
	
	return $form;

}