Still hardcode UC20 amd64 image size, but to the same value as for UC16 and UC18.

debian/changelog

@@ -1,7 +1,11 @@
 livecd-rootfs (2.664.10) UNRELEASED; urgency=medium
 
-  * Do not hard-code the UC20 amd64 image size as now ubuntu-image should be
-    able to properly calculate the needed size itself.
+  * Do not hard-code the UC20 amd64 image size to 8GB as now ubuntu-image
+    should be able to properly calculate the needed size itself.
+  * But per discussion, we might want to keep the UC20 images a bit bigger than
+    what's defined via the gadget/rootfs contents, to make sure writable is
+    comfortably big enough. Use the same hard-coded value as for UC16 and UC18.
+    (LP: #1905990)
 
  -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Fri, 27 Nov 2020 17:58:38 +0100
 

live-build/auto/config

@@ -361,9 +361,8 @@ case $IMAGEFORMAT in
 				pc-amd64|pc-i386)
 					if [ -z "${SUBARCH:-}" ]; then
 						case $SUITE in
-							xenial|bionic)
-								UBUNTU_IMAGE_ARGS="$UBUNTU_IMAGE_ARGS --image-size 3700M"
-								;;
+							# This is to make sure there's enough writable space
+							UBUNTU_IMAGE_ARGS="$UBUNTU_IMAGE_ARGS --image-size 3700M"
 						esac
 					fi
 					;;