ESP32 - how to add files to ota partition

Hi,
I (think I) finally configured the partition table for the ESP-WROVER 16MB correctly with the default_16MB.csv . Now what I’m trying to do is embedding my Webpage-files into the app partition, so that when I do an OTA-Update both the firmware and webpage would get updated simultaneously.
Thats why I used board_build.embed_txtfiles in platformio.ini to embed my HTML and JS files, instead of SPIFFS.
Currently I only have around 800 kB and that works fine.
As the webpage-files will be around 5MB when finished, I tried to simulate it with a dummy JS-file of 3.5 MB.
When building, this is the output:

c:/users/user1/.platformio/packages/toolchain-xtensa32@2.50200.80/bin/…/lib/gcc/xtensa-esp32-elf/5.2.0/…/…/…/…/xtensa-esp32-elf/bin/ld.exe: .pio\build\esp-wrover-kit-16MB\firmware.elf
c:/users/user1/.platformio/packages/toolchain-xtensa32@2.50200.80/bin/…/lib/gcc/xtensa-esp32-elf/5.2.0/…/…/…/…/xtensa-esp32-elf/bin/ld.exe: DRAM segment data does not fit.
c:/users/user1/.platformio/packages/toolchain-xtensa32@2.50200.80/bin/…/lib/gcc/xtensa-esp32-elf/5.2.0/…/…/…/…/xtensa-esp32-elf/bin/ld.exe: region `dram0_0_seg’ overflowed by 970656 b

Does the .embed_txtfiles really store the files in DRAM?
How could I store them in one of the flash partitions (which are around 6.5MB and large enough)?
Also I’d like to update firmware and webpage files simulatenously as mentioned above.
Maybe there is a whole different approach for solving this?

Thanks in advance.

Full platformio.ini and content of custom partition table file if used?

platformio.ini content:

[env:esp-wrover-kit-16MB]
platform = espressif32
board = esp-wrover-kit-16MB
framework = arduino
lib_deps = 
    ESP Async WebServer
monitor_speed = 115200
board_build.partitions = default_16MB.csv

;embedding files: https://docs.platformio.org/en/latest/platforms/espressif32.html#embedding-binary-data 

board_build.embed_txtfiles = 
    data/a.html
    data/b.js
    data/c.js
    data/d.js
    data/e.js
    data/f.css
    data/g.html
    data/h.html

board_build.embed_files = 
    data/font1.otf
    data/font2.otf
    data/font3.otf
    data/font4.otf
    data/favicon.ico

Currently I’m using the default_16MB.csv partition table.
Also I created a new json file for the 16MB Wrover board according to:

Anybody got a hint??