UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.92 Safari/537.36

Steps to reproduce the problem:
1. used chrome option and set argument "--headless","--disable-gpu" and "--start-maximized"
2. launch the browser and get window size using selenium.
3. In headless mode getting size of <800, 600>.
4. Same code in headon mode getting full size <1616,876>.

Chrome Version - 69.0.3497.92
chromedriver=70.0.3538.16

What is the expected behavior?
In headless mode also browser should get fully maximized

What went wrong?
Log :-

HEADLESS MODE

Running TestSuite
11:56:11.244 [main] INFO io.github.bonigarcia.wdm.WebDriverManager - Reading https://chromedriver.storage.googleapis.com/ to seek chromedriver
11:56:12.256 [main] INFO io.github.bonigarcia.wdm.WebDriverManager - Latest version of chromedriver is 70.0.3538.16
11:56:12.266 [main] INFO io.github.bonigarcia.wdm.Downloader - Using binary driver previously downloaded
11:56:12.276 [main] INFO io.github.bonigarcia.wdm.WebDriverManager - Exporting webdriver.chrome.driver as C:\Users\Tanmoy\.m2\repository\webdriver\chromedriver\win32\70.0.3538.16\chromedriver.exe
Starting ChromeDriver 70.0.3538.16 (16ed95b41bb05e565b11fb66ac33c660b721f778) on port 27507
Only local connections are allowed.
Sep 18, 2018 11:56:15 AM org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: OSS
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.assertj.core.internal.cglib.core.ReflectUtils$1 (file:/C:/Users/Tanmoy/.m2/repository/org/assertj/assertj-core/3.3.0/assertj-core-3.3.0.jar) to method java.la
ng.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of org.assertj.core.internal.cglib.core.ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
window size - (800, 600)

Tests run: 10, Failures: 1, Errors: 0, Skipped: 9, Time elapsed: 11.241 sec <<< FAILURE! - in TestSuite
navigateTologinModule(com.test.ui.admin.user.UserUITest)  Time elapsed: 10.945 sec  <<< FAILURE!
org.openqa.selenium.ElementNotVisibleException:
element not interactable
  (Session info: headless chrome=69.0.3497.92)
  (Driver info: chromedriver=70.0.3538.16 (16ed95b41bb05e565b11fb66ac33c660b721f778),platform=Windows NT 6.1.7601 SP1 x86_64) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 0 milliseconds
Build info: version: '3.12.0', revision: '7c6e0b3', time: '2018-05-08T14:04:26.12Z'
System info: host: 'PC', ip: '192.168.2.95', os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '9.0.1'
Driver info: org.openqa.selenium.chrome.ChromeDriver
Capabilities {acceptInsecureCerts: false, acceptSslCerts: false, applicationCacheEnabled: false, browserConnectionEnabled: false, browserName: chrome, chrome: {chromedriverVersion: 70.0.3538.16 (16ed9
5b41bb05..., userDataDir: C:\Users\Tanmoy\AppData\Loc...}, cssSelectorsEnabled: true, databaseEnabled: false, goog:chromeOptions: {debuggerAddress: localhost:51120}, handlesAlerts: true, hasTouchScree
n: false, javascriptEnabled: true, locationContextEnabled: true, mobileEmulationEnabled: false, nativeEvents: true, networkConnectionEnabled: false, pageLoadStrategy: normal, platform: XP, platformNam
e: XP, rotatable: false, setWindowRect: true, takesHeapSnapshot: true, takesScreenshot: true, unexpectedAlertBehaviour: , unhandledPromptBehavior: , version: 69.0.3497.92, webStorageEnabled: true}
Session ID: c6b1becd64aa4ac3c49e237c073f6d4f

Did this work before? Yes 

Chrome version: 69.0.3497.92  Channel: stable
OS Version: 7
Flash Version: