Own compile image - different size for clean compile or recompile

Hi everyone,
I observe that when I compile image on clean environment and have different size versus compile on older build environment only updated via:
git pull

./scripts/feeds update -a
./scripts/feeds install -a
make defconfig
and make -j16

And e.g today I received image size:
22723710 Oct 5 10:43 tmp/openwrt-ramips-mt7621-xiaomi_mi-router-3g-squashfs-sysupgrade-reuse.bin
after executing:
make dirclean and again make defconfig make-j16:

22344830 Oct 5 12:16 tmp/openwrt-ramips-mt7621-xiaomi_mi-router-3g-squashfs-sysupgrade-clean.bin

 22344830 Oct  5 12:16 tmp/openwrt-ramips-mt7621-xiaomi_mi-router-3g-squashfs-sysupgrade-clean.bin
 22723710 Oct  5 10:43 tmp/openwrt-ramips-mt7621-xiaomi_mi-router-3g-squashfs-sysupgrade-reuse.bin